The answer is Guerilla Warfare and the question is about the War in the South, which took place in the 18th century.
In October of 1780, General Gates was replaced by General Nathanael Greene (on the American side). He introduced the new warfare. Instead of attacking Cornwallis (the British)all at once, he decided to use the hit-and-run tactic. Thanks to that, the British were forced to go back to Yorktown, as they were gradually pushed away towards the coast.